Method and apparatus for embedding auxiliary information within original data

ABSTRACT

This patent application is generally related to watermarking and steganography. One claim recites a method of transmarking a media signal previously embedded with a first digital watermark using a first digital watermark embedding method. The method includes: utilizing a programmed electronic processor, detecting the first digital watermark in the media signal; converting the media signal to a different format; utilizing a programmed electronic processor, embedding detected message information from the first digital watermark into a second digital watermark in the converted media signal such that the second digital watermark is adapted to robustness or perceptibility parameters associated with the new format. Of course, other combinations and claims are provided as well.

This application is a continuation of U.S. patent application Ser. No.11/691,938, filed Mar. 27, 2007, now U.S. Pat. No. 7,532,740, which is acontinuation of U.S. patent application Ser. No. 09/404,292, filed Sep.23, 1999, now U.S. Pat. No. 7,197,156. Each of the above patentdocuments is hereby incorporated by reference.

The Ser. No. 09/404,292 application claims the benefit of ProvisionalPatent Application Nos. 60/101,851, filed Sep. 25, 1998; 60/110,683,filed Dec. 2, 1998; 60/114,725, filed Dec. 31, 1998; and 60/126,591,filed Mar. 26, 1999, each of which are hereby incorporated by reference.

This application also relates to U.S. Provisional Patent ApplicationNos. 60/123,587, filed Mar. 10, 1999 and 60/126,592, filed Mar. 26,1999, each of which are hereby incorporated herein by reference. Theapplication also relates to U.S. patent application Ser. No. 09/404,291,filed Sep. 23, 1999, now U.S. Pat. No. 7,055,034, hereby incorporated byreference.

FIELD OF THE INVENTION

This invention relates to the field of signal processing, and morespecifically, to techniques for hiding auxiliary information withinoriginal data.

BACKGROUND OF THE INVENTION

With the recent explosive growth in the use of electronic information,enforcement of copyright laws has become more difficult. The cost of theequipment required to copy digital data representing music, art, andother valuable information has been decreasing, while the capacity ofreadily available data storage media has been increasing. Inexpensivedevices can write enormous amounts of data to digital storage media suchas writable compact disks (CD-R or CD-RWs), multi-gigabyte hard diskdrives, high capacity removable magnetic disks, and soon to be availabledigital versatile disks (DVDs). Readily available high-resolutionprinters and scanners bring the digitization and reproduction of graphicinformation within the means of most consumers. In addition, readilyavailable high-resolution sound cards, including analog-to-digital anddigital-to-analog converters, bring the digitization and reproduction ofaudio information within the means of most consumers. Not only iscopying digital files simple and inexpensive, the Internet facilitatesunauthorized distribution of copyrighted works.

Unlike analog copies, which are always inferior to the original, a copyof digital information can be identical to that of the original, with nodegradation due to copying. Millions of dollars are lost annually due toillegal but exact duplications of digital media and near-exactduplications of analog media. Because copying equipment is readilyavailable, catching persons making unauthorized copies can be difficult.Even if an unauthorized copier is apprehended, the creator of theoriginal document must still prove that the allegedly unauthorized copywas in fact copied from his original work and not independently created.

One approach to solving the problem of illegal copying is embedding orhiding authentication information or copy protection information withinthe original data. Hiding auxiliary information in original data, alsocalled steganography, has been used for thousands of years. Insteganography, a message is hidden within another object or media, sothat the message is minimally perceived by an observer. Steganography isrelated to, but different from, cryptography, in which the existence ofa message is typically obvious, but its meaning is not ascertainablewithout special knowledge.

Hidden data, also referred to as auxiliary or embedded data, can be usedto prevent unauthorized copying by embedding in the original datacommands that are readable by the copying device and that instruct thecopying device not to make a usable copy. Hidden data can also be usedto authenticate data, that is, to prove authorship. One such techniqueentails embedding auxiliary information in an original work in such amanner that special knowledge, such as a secret algorithm or code, isrequired to detect and/or remove the auxiliary information. The copierwould not be able to remove the authentication information, and theoriginal creator could prove his authorship by retrieving the embeddedinformation, which would identify him as the author.

Data hiding has uses besides the prevention and detection ofunauthorized copying. One such use is content enhancement, that is,adding information to the original data to enhance the content. Forexample, lyrics could be embedded in audio data on a CD. The lyricscould be viewed in a special karaoke machine, while the audio could beplayed on an existing CD player. Hidden data could also be used toassociate different segments of video data with differentviewer-selectable versions of the video on a DVD. For example, a viewercould select between a version edited for children or an unabridgedversion, and embedded auxiliary data would indicate to the DVD playerwhich video segments to skip and which to include for the selectedversion.

The original data in which the auxiliary data is hidden may representany type of information that is perceivable with the aid of a presentingdevice. For example, the data may represent music which is presentedusing a compact disk or audio DVD player, a video film that is presentedon a DVD player, or an image that is presented on a computer screen or aprinter.

When the combined data is presented to a user by a normal presentationdevice, the auxiliary data should not interfere with the use of theoriginal data. Ideally, the user should not be able to perceive theauxiliary data at all. Unfortunately, increasing the amount of theembedded auxiliary data or its robustness, that is, its persistence toattack and data transformation, may incidentally increase itsperceptibility. The degree to which the auxiliary data can be perceivedwithout having an adverse impact on the user varies with theapplication. For example, in CD quality audio, a minor change from theoriginal data might result in unacceptable audio artifacts. In videodata, a minor change in a presented image may be acceptable, even thoughthe change might be noticeable if the original and combined works arepresented and compared side by side.

Several techniques are known for hiding auxiliary information inoriginal digital data. Data can be hidden in original data as headers ortrailers appended to the original data. Such techniques are of limiteduse in protection of copyrighted works, because the auxiliary data iseasily located and stripped out of the copy, as when changing format.More sophisticated techniques distribute the auxiliary data through theoriginal data, entwining the auxiliary and original data until theauxiliary data is difficult, or even statistically impossible, toidentify and strip from the the combined data.

Most data hiding techniques that distribute the auxiliary data throughthe original data are computationally intense and therefore expensive toimplement. Many of these techniques are based upon adding or subtractingperiods of pseudo-random noise (PN) sequences with the signal torepresent the auxiliary information, and these sequences may requirefiltering (a.k.a. shaping) in the frequency domain. The rest are basedupon adding the auxiliary information to the original data after theoriginal data has been transformed into the frequency domain, such as bya Fourier transform. Auxiliary information can be added in the frequencydomain so that the energy of the auxiliary data is spread across manyfrequencies in a manner similar to that of the PN sequence. In addition,auxiliary information can be added to the phase of the frequencycomponents with and without spreading the information acrossfrequencies. Unfortunately, transforming the data into the frequencydomain and/or shaping the energy of the PN sequence so it is lessperceivable requires intense calculations.

The ability of users to detect auxiliary data depends not only upon thedata, but also upon the characteristics of the human sense organs andthe interpretation of sensory stimuli by the brain. Some data hidingtechniques transform the original data into the frequency domain andembed auxiliary data in a manner such that the frequency spectrum of theoriginal data reduces the perception of embedded data. Thispsychophysical effect is known as masking. The frequency distribution ofthe original data is used to determine preferred frequencies at whichthe embedded auxiliary data will be less perceptible, that is, masked.Others use the fact that we don't perceive phase as accurately asmagnitude in the frequency domain.

There are some data embedding techniques that are less computationallyintense and that still distribute the auxiliary data in the originaldata. Such techniques include amplitude modulation, frequency bandelimination, distinct quantization, and least-significant bit (LSB)replacement. These techniques embed data in predetermined locationswithout regard to the original data and are, therefore, more likely toproduce perceptual side affects in the combined data. In addition, theLSB replacement technique is easily disturbed by low level noise.

The ease of retrieving embedded data varies with the technique used forembedding. Some data hiding and retrieving techniques retrieve theauxiliary data by comparing the combined data with the original data.Others retrieve the auxiliary information using databases of the PNsequences that were originally used to hide the data. Techniques thatrequire that a copy of the original data or a PN database be used toextract the auxiliary data are of limited use in applications in whichthe combined data is distributed broadly. Such techniques are useful insome applications, such as data authentication, in which the auxiliarydata is retrieved rarely and only by the copyright owner.

Thus, it would be desirable to have a data hiding and extractingtechnique that is not computationally intense and that maintains adesired level of perceptibility and robustness, and in which theembedded data that can be retrieved from the combined data withoutaccess to the original data.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod and apparatus of data hiding and retrieval.

An advantage of the present invention is its extreme efficiency relativeto the prior art. Thus, the apparatus is less expensive.

Another advantage of the invention is that it does not require theoriginal file or other database for extracting the auxiliary data.

Another advantage of the invention is that it uses an adaptive algorithmbased upon psychophysics. Specifically, the invention uses the originaldata, in unmodified form or without complex data transformations, todetermine the location to insert auxiliary data.

A further advantage of the invention is that, in some embodiments, theembedded data can be imperceptible when presented with existing players.

Still another advantage of the invention is that usually it uses abroadband approach that distributes the auxiliary data through theoriginal data, thereby making the auxiliary data more difficult todetect and remove.

Yet another advantage of the invention is that it provides for a minimaldecrease in signal-to-noise ratio (SNR) of the combined data as comparedto the original data.

Still a further advantage of the invention is that it provides non-LSBcapabilities, thereby providing increased robustness, that is, theauxiliary data is unchanged by some transformations of the combineddata.

Yet a further advantage of the invention is that it can cause nodetectable change in data's statistics, thereby making authenticationinformation impossible to identify.

Still another advantage of the invention is its versatility, in that itallows the user to set parameters that vary the perceptibility,robustness, and embedding rate so that the invention can be used in abroad variety of applications.

The apparatus for the present invention includes a logic processor andstorage unit, such as those that come with the standard computer or onDSP boards. These devices will act as data readers, comparer and datawriters, such the user's desired watermark can be embedded and/orretrieved.

The process involves embedding and retrieving auxiliary information intooriginal data to produce combined data. The invention uses a detectioncriterion or criteria to determine where in the original data to locateand adjust data points to carry the auxiliary information. The detectioncriteria is used to locate positions, referred to as local maskingopportunities, in the original data at which the embedding of auxiliarydata will produce less perception, as compared to other simplisticprocesses. When embedding the auxiliary data, the data points in theoriginal data are investigated in accordance with the detection criteriato determine the existence of local masking opportunities. The detectioncriterion or criteria may involve, for example, comparing the data pointto a predetermined value and examining the relationship of the datapoint to nearby points. If the detection criteria are met, one or moreof the nearby points, or the data point being investigated, is changedto indicate the value of an embedded bit of auxiliary data.

Thus, although the search for local masking opportunities typicallyprogresses point by point through the data, the investigation of eachpoint may include not only the value of that point, but also values ofone or more nearby points and/or one or more relationships among thepoints. If the investigation of a point shows the existence of a localmasking opportunity, data is embedded by setting the value of one ormore of the local points, that is, either the point being investigatedor one or more of the nearby points.

The value to which the nearby data points are set is typically dependentupon the data point being investigated as well as on the value of theauxiliary data bit. The data point value can be set so that it has aspecified relationship with the neighboring data points. The process iscontinued until the original data has been traversed or no additionalauxiliary data remains to be embedded.

Retrieving the auxiliary data is the inverse of the embedding process.The combined data is traversed using the detection criteria to locatethe local masking opportunities. As each local masking opportunity islocated, the nearby data point or points that was or were set toindicate the embedded bit is or are read to extract the embedded data.The process is continued until the combined data has been traversed.

In the preferred embodiments, a data point or points are set to a valuerelative to the nearby data points and not to an absolute value. Bothsetting data points at the local masking opportunity and setting thedata point to a value related to the nearby points, rather than to avalue unrelated to the original data, provide masking that reduces theperceptibility of the data. The data is extracted by determining therelationships or values of the point or points near the local maskingopportunity.

For the two preferred embodiments described in detail below, only pointswith large values are adjusted, and by a minimal amount; thus, theseembodiments are based upon the masking of a weak stimulus by an intensestimulus. The process is applicable to analog and digital data. However,both embodiments are explained in terms of digital media due to currentswitch to digital media and the ease of understanding.

Specifically, the first preferred embodiment uses the difference betweena data point after a peak and the peak level to carry auxiliaryinformation, as long as the peak is above a large threshold and theoriginal difference between the peak and next point is not too great.This large threshold and minimal differences produce the desiredperceptual masking. The embedding process adjusts the point after theabove-threshold peaks to hide the auxiliary data. Correspondingly, theretrieving process measures the difference between each above thresholdpeak level and the next data point to retrieve the auxiliary data.

The second preferred embodiment uses the change in slope across apositive, large, steep, threshold crossing to hide the auxiliaryinformation, as long as the original change in slope is not too greatyet steep enough to accept the ensuing adjustment. Again, the largethreshold produces the desired perceptual masking. In theimplementation, the embedding process adjusts the change in slope toembed the data, whereas the retrieving process measures the change inslope to obtain the auxiliary data.

Usually, the preferred embedding process implicitly spreads the energyof the auxiliary information throughout the original data. Thisbroadband approach produces data that is more difficult to remove thansub-band approaches that place the data in an inaudible in an inaudiblefrequency range. If desired, parameters can be chosen so that theprocess produces protected data that is statistically identical tounmarked data. Importantly, the process can be adjusted to produce thedesired tradeoffs between perception, coding rate and robustness toattack.

Such embodiments of the invention preferably operate on the originaldata without requiring any complex data transformations, such as aFourier transformation. Thus, if the original data representsinformation in the time domain, the data can remain in the time domainas the auxiliary data is embedded and retrieved. Of course, theinvention can operate on original data of all types, such as in thefrequency or time-frequency domain. For example, it can be applied toMPEG data, including the MPEG 1 and 2 specification, ISO 11172-3 and ISO13818-7 respectively, herein by reference, which exists in thetime-frequency domain.

Finally, the problem of bit-rate reducing techniques, known ascompression, removing the watermark can be bypassed by using separate,but possibly identical, watermark procedures during the compression(a.k.a. encoding) and decompression (a.k.a. decoding) process.

In summary, the present invention has the advantage of being extremelyefficient to implement while still maintaining a desired level ofrobustness, i.e., resistance to tampering, including non-LSB (leastsignificant bit) capabilities and statistical invisibility. Theefficiency of the present invention means that it is cheaper toimplement and can be used to embed, retrieve and search more files thana computationally intense algorithm. Further objects and advantages willbecome apparent from a consideration of the ensuing description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing, in general, the steps embedding datausing the invention.

FIG. 2 is a block diagram showing an apparatus used to embed or retrievedata using the process of FIG. 1.

FIG. 3 is a flowchart showing, in general, the steps used to retrievethe data embedded using the process of FIG. 1.

FIG. 4 graphically displays the operation of a first embodiment of theinvention.

FIG. 5 is a flowchart showing the steps of embedding data in accordancewith the first embodiment of the invention. The dashed lines showinteraction with the auxiliary data.

FIG. 6 is a flowchart showing the steps of retrieving data that wasencoded in accordance with the embodiment shown in FIG. 5. The dashedlines show interaction with the auxiliary data.

FIG. 7 graphically displays the operation of a second embodiment of theinvention.

FIG. 8 is a flowchart showing the steps of embedding data in accordancewith a second embodiment of the invention. The dashed lines showinteraction with the auxiliary data.

FIG. 9 is a flowchart showing the steps of retrieving data that wasencoded in accordance with the embodiment shown in FIG. 8. The dashedlines show interaction with the auxiliary data.

FIG. 10 demonstrates the operation of the invention in conjunction withdigital compression techniques.

FIGS. 11 A and B are two block diagrams showing an embedding andretrieving apparatus used to carry out the invention.

FIG. 12 shows an embodiment of the apparatus of FIG. 2 for embeddingdata.

FIG. 13 is a block diagram showing an embodiment of the apparatus ofFIG. 2 for retrieving the data.

DETAILED DESCRIPTION

The system according to a preferred embodiment of the present inventioncomprises a method and apparatus for hiding auxiliary information (ordata) in original data and for retrieving the auxiliary information.

FIG. 1 is an overview of the steps involved in carrying out a method ofthe invention to embed data. FIG. 2 shows a block diagram of anapparatus 10 used to perform the method of FIG. 1. Apparatus 10 includesa logic processor 14, which can be a general purpose microprocessor,such as an Intel Pentium or DEC Alpha, of the type a personal computeror engineering workstation, a digital signal processor (DSP), such thehte Texas Instruments TMS320 line, a specialized CPU, such as a mediaprocessor, or a custom processing circuit. Apparatus 10 also includes astorage unit 18, which can include random access memory (RAM) or delays.Because the algorithms used by the invention are not computationallyintense, they require calculations on the order of less than one millioninstructions per second and can be performed by most modern personalcomputers.

The original data mentioned below might represent sound that is recordedby sampling its amplitude periodically, with each sample using binarynumbers to represent the magnitude of the sound at a particular time.Alternatively, the original data could be any series of binary dataassociated into groups. Similarly, the auxiliary information is any datathat can be represented as “1”s and “0”s.

FIG. 1 shows that in step 20, a portion of the original data is readinto storage unit 18 of FIG. 2. Step 24 shows that the sample data isinvestigated sequentially by the logic processor 14 to locate samplepoints that meet predefined detection criteria. Such sample pointsindicate the existence of “local masking opportunities,” because thedetection criteria are such that a change in the value of the sample ora few samples at or near that point to embed auxiliary data will usuallyhave minimal perceivable by the listener of the sound. The amount ofmasking will depend upon the data type and settings chosen by the user.For example, the masking will be great for uncompressed audio and lessfor bit-rate reduced (digitally compressed) audio such as MPEG. The samedetection criteria will be applied during data retrieval to locate thehidden data.

Each point in the original data is preferably investigated to determinewhether it represents a local masking opportunity. The criterion orcriteria for determining local masking opportunities may entail not onlythe value of the point being investigated, but may also include thevalue of at least one nearby or neighboring point, or the relationshipbetween the nearby point and the point being investigated. The detectioncriteria can require, for example, that the point being investigatedexceeds a certain threshold value and/or that the point be a localmaximum or peak. The criteria may include a requirement that a pointsubsequent to the point being investigated have a value that differsfrom the point being investigated by less that a prescribed amount, orhave some other relationship to the point being investigated.

The sample data points can be considered as plotted on a graph, forexample with time on the x-axis and the and the magnitude of the sampleon the y-axis. Thus, the series of data points can be considered ashaving a slope between any points, and the value of the slope can bepart of the detection criteria. The criteria may specify, for example,that a slope defined by the point being investigated and a precedingpoint exceed a particular value, or that the change in slope before andafter the point not exceeds a particular value. The criteria couldinclude any combination of requirements. The threshold criteria can bechanged to meet the needs of specific applications without departingfrom the concept of the invention.

In each case, no complex data transformation is required to mask theauxiliary data, so comparing a point to the detection criteria isrelatively quick and inexpensive. Unlike prior art methods, which needto use distant points to convert the original data into the frequencydomain to determine how to mask embedded data, the present invention candetermines masking opportunities using only nearby or neighboringpoints, that is, points that are too close to use to determine usefulfrequency data. Nearby points including points that are next to thepoint being investigated or within a relatively small number of points,preferably less than 50 and more preferably less than 20. The criterioncan be as simple as determining whether the point exceeds a threshold.

Step 26 shows that when a point meeting the detection criteria islocated, the value of a specified sample point or sample points near thelocal masking opportunity is changed to reflect the value of theauxiliary information to be embedded. Although the changed sample may besimply set to a particular value to signify the value of the embeddedbit, the new value typically depends upon the value of both theauxiliary data and the neighboring point or points that wereinvestigated to detect the local masking opportunity. For example, thepoint may be set so that the change in value or slope signifies whetherthe embedded bit is a “1” or a “0”.

When a point is set to its new value, it is important that either thechange does not prevent the original sample point from continuing tomeet the detection criteria, or that this local masking opportunity isskipped and not detected in the retrieval process. Otherwise, theembedded auxiliary data will not be retrievable.

Alternatively, it is possible to merely embed the auxiliary bit as theleast significant bit, or other, preferably low order, bit. The embeddedbit is still masked because the location of the embedded bit was chosento represent a local masking opportunity, such as when the data islarger than a prescribed threshold.

Step 30 shows that the process is ended at step 32 if no additionalauxiliary data needs to be embedded. Otherwise, step 34 shows that ifthere is additional data in memory, the search for local maskingopportunities continues. Step 36 shows that if all data in memory hasnot yet been searched, additional data is read into memory. Skilledpersons will recognize that some overlap of the data in memory isrequired to prevent missing local masking opportunities that occur atthe beginning or end points of the data in memory.

FIG. 3 broadly shows the steps involved in carrying out a method of theinvention to detect and retrieve the embedded auxiliary information.Because the same processor and memory that was used to embed the datacan be used to retrieve the data, although not necessary, the steps ofFIG. 3 will describe extracting data using data using the hardwarecomponents of FIG. 2. Step 50 shows that a portion of the original datais read into storage unit 18. Step 52 shows that logic processor 14investigates each data point to determine the existence of a localmasking opportunity. If a sample point meets the local maskingopportunity criteria, step 54 shows that the embedded “1” or “0” bit ofauxiliary data is extracted using the inverse relationship of how theauxiliary data was embedded. Step 56 shows that if additional combineddata is in the memory, the logic processor continues to investigate theremaining points with step 52. Step 58 shows that if all the data inmemory has been investigated, but there is uninvestigated combined datain the data file, additional data is read into memory in step 50. Step60 shows that the process is ended when all the combined data has beeninvestigated.

Two preferred embodiments are described briefly here, and in detailbelow, to demonstrate the flavor of this methodology. As shown in FIG.4, the first embodiment uses large, positive peaks as the detectioncriteria 120 and the auxiliary information is stored in the difference130 between the peak and the next point. As shown in FIG. 7, the secondembodiment uses large, steep threshold crossings with minimal change inslope as the detection criteria 140, and the auxiliary information 150is carried in the change in slope.

The methodology is applicable to analog or digital data, even though thepreferred embodiments use digital data. For example, analog data can besampled at the Nyquist rate to produce digital data in which additionalinformation is hidden. Then, the combined digital data can be returnedto the analog domain by any existing method known in digital signalprocessing (DSP). The analog data now contains the embedded data, whichcan be which can be decoded by using sampling. This is just one possiblemethod to encode analog data with the above methodology.

The methodology is also applicable to audio, speech, images, video orany other perceivable signal. With audio and speech, the original datacould represent pressure versus time, magnitude versus frequency, or aspecific frequency magnitude versus time. With images, the original datacould represent gray code versus space, separate or combined RGB orequivalent values versus space, or magnitude versus frequency. Videodata encompasses the image data with an added dimension of timeavailable. For example, with MPEG bit-reduced audio or images theauxiliary data could be embedded in scaling factors or frequencycoefficients versus frequency or time or both.

Usually one of the detection criteria is a large threshold. With 16 bitaudio, a threshold greater than 48 dB above the minimum value isdesirable. This threshold allows the data to be changed with minimalperception due to masking. Masking is the psychological term defined asthe increase in threshold for steady-state stimuli. Use of the term inthis invention is much broader than that definition, and describes howone set of data reduces the perception of other data. Specifically, foruncompressed, magnitude-time data, the sensitivity of the sensory systemdecreases with increased input level, thus the small adjustment of anneighboring data point is masked by the large value of the threshold.For bit-rate reduced, time-frequency data, such as MPEG data, themasking is minimal and more similar to the textbook definition sincemasking has been used to reduce the bit rate.

Finally, this method is applicable to data where masking is not used,but the efficiency of the process in that it is does not require a key,such as a PN sequence, or original data for retrieval of the auxiliaryinformation, is an advantage. In summary, the parameters of thedetection criteria will determine the interaction between the data rate,process complexity and perceptual quality.

Embodiment 1

The first preferred embodiment is based upon hiding the auxiliaryinformation in large peaks within the original data. In this embodiment,the auxiliary information is preferably broken into N bit words, withsynchronization data placed between the words for better error recovery.The auxiliary information does not need to include sync pulses betweenthe words if robustness to noise or modified files is not needed.

FIG. 4 conceptually shows that the first embodiment detects a peak orlocal maximum and sets the value of the subsequent point in relation tothe peak to indicate the value of the embedded bit.

FIG. 5 includes the pseudocode in the form of a flowchart for theembedding process. The process begins by searching the original datauntil a positive peak that lies above a large threshold, labeled thr,and has a relatively small decrease after the peak, labeled dS, isfound. This process is demonstrated in boxes 200, 210 and 220. Thedetection criteria are checked in the most computationally efficientorder, which includes first checking to see if the point represent apeak since peaks are the least likely criterion.

When a desirable peak is found, the data point after the peak isadjusted according to a user defined bit depth, b, to carry theauxiliary information. Specifically, if it is the beginning of anauxiliary word, the synchronization code is embedded by adjusting thepoint after the peak, x[n+1], to be equal to the peak, x[n], minus halfof the maximum allowable change, dS/2, between the peak and the nextpoint, as shown in boxes 242, 230 and 250. An auxiliary information bitof one is encoded by adjusting the point after the peak, x[n+1], to beequal to the peak, x[n], minus half the maximum change, dS/2, and plusthe half the bit depth magnitude, 2^(b−1). Correspondingly, an auxiliaryinformation bit of zero is encoded by adjusting the point after thepeak, x[n+1], to be equal to the peak, x[n], minus the sum of half themaximum change, dS/2, and half the bit depth magnitude, 2^(b−1). Thisembedding of zeros and ones is shown in boxes 242, 240, 260, 270 and280. The next two points after embedding the data should be skipped soone does not create another peak for very slow changing (i.e. flat)data, as shown in box 290.

These steps are repeated until the auxiliary information, box 242 and240, has been hidden in the original data or the original data isfinished.

FIG. 6 displays the pseudocode in the form of a flowchart for theretrieval process of the first preferred embodiment. The process beginsby searching the original data is searched until a positive peak thatlies above a large threshold, labeled thr, and has a relatively smalldecrease after the peak, labeled dS, is found. This process isdemonstrated in boxes 300, 310 and 320. Again, the search first looksfor a peak to improve efficiency.

When a desirable peak is found, the difference between the peak and thedata point after the peak is measured to retrieve the auxiliaryinformation. Specifically, if the peak minus the point after the peak,x[n]−x[n+1], is close to half of the maximum allowable change, dS/2, anew auxiliary word is beginning, as shown in boxes 330 and 350. If thepeak minus the point after the peak, x[n]−x[n+1], is approximately equalto half the maximum change, dS/2, minus half the bit depth magnitude,2^(b−1), an auxiliary bit of one is found. If this difference,x[n]−x[n+1], is close to the sum of half the maximum change, dS/2, andhalf the bit depth magnitude, 2^(b−1), an auxiliary bit of zero isretrieved. This retrieving of zeros and ones is shown in boxes 340, 360,370, 380, and 382. The two points immediately after retrieving the datacan be skipped as shown in box 390.

These steps are repeated until the auxiliary information has beenretrieved in the original data or the original data is finished.

There are three user-defined parameters, including threshold, thr; bitdepth, b; and maximum allowable change after the slope, dS. For 16 bitaudio, the threshold is usually around 48 dB above the minimalquantization, as discussed above. For data with more bits per sample,the threshold may be increased to reduce perception. The bit depth is anindication of the relative change to be made to the sample point toembed the data. Thus, the smaller the bit depth, the less disturbance ofthe original data, making the embedded data less perceptible to thelistener, but less robust, that is, more susceptible to being lost tonoise or attack. Minimal perception in 16 bit audio is found when bitdepths are between 1 and 6 bits. However, higher bit depths can be usedif one desires more robustness to noise in trade for more perceptualdegradation. The maximum allowable change after the peak, dS, must be atleast the desired bit depth magnitude, 2^(b). On the one hand, one cangain better robustness to noise at the expense of more distortion, if dSis set to twice the bit depth magnitude, 2^(b+1). On the other hand, ifone desires to keep the threshold undetectable to statisticalcryptoanalysis (labeled statistically invisible), dS should be set at2^(b), and b should be small, probably below 3 bits. If dS is not 2^(b),one can use the discrepancy of the average difference between largepositive peaks and their next points between embedded file and regularfile data to determine if the file contains embedded data or not.Finally, if dS is much greater than 2^(b), the auxiliary informationembedding rate will be increased, because more peaks will be foundsuitable for data embedding. Using the principles explained above,skilled persons will be able to set the user-defined parameters tovalues appropriate to the requirements of a particular application.

As discussed above, the large threshold usually reduces the perceivableeffect of adding the auxiliary information, and may even cause theauxiliary data to be non-perceivable, depending upon the data type. Inaddition, many data points satisfy the small difference between the peakand data point after the peak, because with a slope near 0 at the peak,the data is changing the least. This small difference means that theadjustment will be small as compared to the threshold, thus reducing thechance of perceiving the embedded auxiliary data

The pseudocode is shown using a buffer with what appears to be lookahead capabilities (i.e. x[n+1]). This makes the process easier toexplain and understand. However, the process is causal, as determined byreplacing n+1 with k, and keeping track of the last two points, x[k−1]and x[k−2].

Finally, one can add more criteria to define the peak. For example, thepeak extends for one more point each direction where x[n]>x[n−2],x[n]>x[n+2], x[n]>x[n−3], x[n]>x[n+3], and so on, or the peak is ofminimal sharpness, i.e. x[n]−x[n−1]>5. Both of these criteria producebetter robustness to noise and less distortion since it will take morenoise to move the location of the peak, although changes in the peakcriteria affect the rate at which auxiliary data can be embedded.

The embedded data density and bit rate will vary with the original dataand with the user-defined parameters. For example, bit rates of between99 and 268 bits per second were achieved in CD quality audio data usinga bit depth of 5 and a threshold of 5,000 (74 dB). Using a bit depth of8 and maintaining a threshold at 5,000, the average embedding rate was1,000 bits per second. When the threshold is lowed to 2,000 at a bitdepth of 8, an average embedding rate of 2,000 bits per second wasfound.

Embodiment 2

The second preferred embodiment hides the auxiliary information inlarge, steep threshold crossings which do not have a large change inslope. The method is more robust to noise changing the detectedlocation. This occurs because it is less likely that noise changes thelocation of a threshold crossing as compared to a peak, since athreshold crossing usually has a slope larger than the slope at thepeak, which, by definition, has a slope near zero. Testing with audiodata has shown this embodiment, as compared to the first embodiment, toproduce a lower embedded data rate and is more perceivable at a lowerbit depth, in trade for the robustness to noise. One will probably findthe optimal embodiment dependent upon the application.

upon the application.

FIG. 7 conceptually shows that data is embedded by setting the slopeafter the threshold crossing in relation to the slope at the thresholdcrossing.

In FIG. 8, the pseudocode for hiding the auxiliary information using thesecond preferred embodiment is presented in the form of a flow chart.The process begins by searching the original data until a positive,large, steep threshold (labeled thr) crossing with minimal change inslope (labeled dS) is found. This process is demonstrated in boxes 400,410 and 420.

When the desirable threshold crossing is found, the data point after thethreshold crossing is adjusted according to a user defined bit depth (b)to carry the auxiliary information in the change in slope. Note that thechange in slope is defined as (x[n+1]−x[n])−(x[n]−x[n−1]), orequivalently as x[n+1]−2*x[n]+x[n−1]. Specifically, if it is thebeginning of an auxiliary word, the synchronization code is embedded byadjusting the point after the threshold crossing, x[n+1], so that thechange in slope is zero, as shown in boxes 442, 430 and 450. Anauxiliary bit of one is encoded by adjusting the point after thethreshold crossing, x[n+1], so that the change in slope is positive byan amount equal to half the bit depth magnitude, 2^(b−1).Correspondingly, an auxiliary bit of zero is encoded by adjusting thepoint after the threshold crossing so that the change in slope isnegative by an amount equal to half the bit depth magnitude, 2^(b−1).This embedding of zeros and ones is shown in boxes 442, 440, 460, 470and 480. The point after embedding the data can be skipped forefficiency as shown in box 490.

These steps are repeated until the auxiliary information has been hiddenin the original data or the original data is finished.

FIG. 9 shows the pseudocode in the form of a flowchart for the retrievalof the auxiliary information in the second preferred embodiment. Theprocess begins by searching the original data until a positive, large,steep threshold (labeled thr) crossing with minimal change in slope(labeled dS), is found. This process is demonstrated in boxes 500, 510and 520.

When a desirable threshold crossing is found, the change in slope aroundthe threshold is measured to retrieve the auxiliary information. Again,the change in slope is defined as (x[n+1]−x[n])−(x[n]−x[n−1]), orequivalently as x[n+1]−2*x[n]+x[n−1]. Specifically, if the thresholdcrossing has almost zero change in slope, a new auxiliary word is begun,as shown in boxes 530 and 550. If the threshold crossing has a positivechange in slope approximately equal to half the bit depth magnitude,2^(b−1), an auxiliary bit of one is found. If the threshold crossing hasa negative change in slope approximately equal to half the bit depthmagnitude, 2^(b−1), an auxiliary bit of zero is retrieved. Thisretrieving of zeros and ones is shown in boxes 540, 560, 570, 580, and582. The point after retrieving the data can be skipped for efficiencyas shown in box 590.

These steps are repeated until the auxiliary information has beenretrieved in the original data or the original data is finished.

As mentioned above, one does not want the embedding process to eliminatethe embedded location from fulfilling the detection criteria.Specifically, in this embodiment, the pre-threshold change condition,x[n]−x[n−1]>dS+2^(b−1), in the detection criteria of box 420 and 520requires that the adjustment of the next data point does not bring thepoint back below the threshold. An alternative approach, is to ignorethis condition and condition and to set either the current or next point(x[n] or x[n+1], respectively) to the threshold if the embedding processwould cause the next point to move below the threshold, and ignore anydata points that are equal to the threshold in both the embedding andretrieving process. Interestingly, only when embedding a sync or 0 couldthe next point move below the threshold. Given these options, thedescribed embodiment is chosen so the process is causal, thusincorporating the known advantages of causal processes.

Once again, the large threshold and maximum allowable change in slopecondition, dS, reduce the perception of embedding the auxiliary data,and depending upon the data type can cause the embedding process to becompletely non-perceivable. The maximum allowable change in slopecondition, dS, can have any value. A larger value allows a higher datarate with more perceivable distortion, whereas a smaller value producesminimal distortion with a lower data rate. Our preferred setting for dSin 16 bit audio is equal to the bit depth magnitude, 2^(b). Again, bitdepths below 6 bits produce minimal distortion, but higher bit depthscan be used for robustness to noise and attack.

Using a threshold of 2,000 (i.e. 66 dB) and a bit depth of 5, data ratesbetween 40-100 bits per second are expected, with an average of about 75bits per second, for CD quality audio. At a bit depth of 8, the bit rateincreases to an average of 100 bits per second.

Modifications

The preferred embodiments have been described in detail above. However,there are many simple modifications that can be made to optimize theprocess for each use. Thus, these modifications and many similar onesproduce a process that is equivalent to the one taught in thisdisclosure.

In some applications, a very simple embodiment could use a simplethreshold to determine a local masking opportunity and then encode theauxiliary data in the LSB of the point exceeding the threshold or ofanother point in the vicinity of the point exceeding the threshold. Sucha variation is extremely simple, yet provides reduced perceptibilitycompared to prior art LSB schemes. As with the other embodiments, onemust ensure that changing the value does not remove the point for thedetection criterion. In this case, one could simply skip embedding wherethe change brings the data below the threshold, and change the currentvalue of the data point to the threshold so that the data point will beskipped in the retrieving phase.

To increase the robustness of the invention to attack or noise, thefollowing changes could be made. (Attack is defined as a person ormachine trying to remove the auxiliary information from the combinedsignal without distorting the perception of the original data.)

Using a dynamic threshold can make it harder to remove the auxiliaryinformation. An example dynamic threshold is an offset sinusoidalwaveform. When using a dynamic threshold, dS should be small and closeto 2^(b) so that the process does not change the distribution of thedifferences between neighboring points, i.e. be statistically invisible;thus, an attacker cannot use this data to find the threshold.

One can also use the statistical gaps when dS is larger than 2^(b) tofind the threshold if the attack uses a DC shift. A DC shift isobviously a more potent attack for the second preferred embodiment thanthe first, but could affect the first preferred embodiment sincethreshold is one of the detection criteria.

The process could use more global definitions for peaks and thresholdcrossings, for better robustness to noise. Specifically, a peak orthreshold crossing definition that includes more points on each side.

Finally, the process can use any type of error correction in theauxiliary information to increase the robustness.

To increase the data rate, the following changes could be made. Theauxiliary information does not need to include the extra sync pulsesbetween the N-bit words, especially if robustness to noise is notneeded. In addition, negative going peaks and/or more thresholds can beused to increase bit rate. Finally, the process can use more than abinary system in adjusting the second bit to encode more information.However, the result is more likely to be perceivable or less robust toattack.

An interesting twist is to embed different auxiliary information onpositive and negative peaks, and/or on various thresholds. In addition,with stereo files, you can code the channels separately or move betweenchannels with consecutive points moving between left and right channels.

A change that could improve the perception is to move the data pointafter the embedded point towards the value of the embedded point ifcombining the auxiliary information causes a large value change in theembedded point.

As mentioned above, the data does not have to be relative to time. Forexample, the data could represent magnitude versus frequency. Inaddition, the data could be viewed as magnitude of a specific frequencyversus time. You could include all frequencies for an increased datarate. In other words, you could embed in words, you could embed in thespectrum or spectrogram. Advantageously, you don't have to change theformat of the given data to use this process and correspondingapparatus.

For example, for bit-reduced data, such as MPEG compressed data.MPEG-compressed data comprises a series of data points that representscaling factors and frequency coefficients. The invention could embedauxiliary data in the series of MPEG data points, using, for example,one of the two embodiments described above. When using the firstpreferred embodiment, one may want to increase the peak or modify itsLSB such that the term is only increased, rather than decrease the pointafter the peak, such that quantization error is not increased in theMPEG data, especially when dealing with scaling factors. Skilled personswill recognize that, in using data like MPEG data that is divided intotime frames, one could use, for example, scaling factors or frequencycoefficients from consecutive frames, as well as data pointsrepresenting scaling factors and coefficients of different frequencieswithin a frame, when determining where to embed data. For example, thecoefficients for a particular frequency in consecutive frames could beconsidered as a series of consecutive data points, and those data pointsanalyzed in accordance one of the embodiments above to determine whereto embed data in the series. In an alternative example, the series ofdata points representing scaling factors or frequency coefficients fordifferent frequencies within a frame can be analyzed in accordance withthe first or second embodiment above to decide where to embed data.

The benefits of the inventions can be obtained using any series of datapoints, which can be analyzed to determine where to embed data, althoughthe degree of masking may vary depending upon what the data pointsrepresent.

Example Utilizations

Below are included some example utilizations of the algorithm to aid inits understanding. This list is not complete, and only highlights theusefulness of the invention. The invention in its various forms isuseful in any application in which it is desirable to embed auxiliarydata into original data in a minimally perceptible or imperceptiblemanner.

The process can be used to embed copyright information. This informationcould include a code to determine if the data can be copied. Copyingdevices, such as CD writers, could include an inexpensive integratedcircuit that could interpret to embedded data and prohibit copying.

In addition, author's or artist's name and affiliation can be embedded.In this utilization, the auxiliary information is small and would berepeated over and over with synchronization pulses between eachduplication. Alternatively, the copy code could be embedded usingembodiment 1, and the creator's name and affiliation using embodiment 2.

The invention can also be used to send additional information. Thisinformation could be transmitted in ASCII or ANSI with 8 bit “words”(not to be included with digital words being defined as 32 bits) andsynchronization pulses between these words, if desired. The informationcould be a secret message, lyrics to the song, or a description of theartwork. For lyrics, this could be useful for karaoke machines and CD orDVD players.

Digital Compression

The main problem with hiding data and digital compression (reducing bitrate not dynamic range) is that the process of hiding data isincompatible with digital bit-rate reducing techniques known ascompression (a.k.a. encoding and decoding). This incompatibility occurssince the goal of data hiding is to make the data minimally perceivableand the goal of compression is to remove minimally perceivable parts.

To this end, FIGS. 10A and B demonstrates the process for data hiding,if at some point the data must be compressed. For example, this mayhappen while transmitting the data.

In FIG. 10A, the auxiliary information is embedded in the non-compresseddata using the described invented process or any other appropriatemethod, as shown in box 600. Then, when the data needs to be compressed,the auxiliary information is retrieved via the described invention orthe other appropriate method, and re-embedded in the compressed datawith the described invented process or the other appropriate scheme, asshown in box 610. The algorithm for data hiding in the compressed andnon-compressed data may be the same algorithm, differing by only usingdifferent original data.

In FIG. 10B, the auxiliary information is retrieved from the compresseddata using the described invented process or any other appropriatealgorithm, the data is uncompressed, and the auxiliary information isembedded in the uncompressed data using the described invention or theother appropriate process, as shown in box 620. Finally, when needed,the auxiliary information can be retrieved from the data using thedescribed invention or the other appropriate algorithm, as shown in 630.Once again, the algorithm for data hiding in the compressed for datahiding in the compressed and non-compressed data may be the samealgorithm, differing by only using different original data.

Apparatus

As described above, FIG. 2 demonstrates that the invented process can beimplemented via logic processor and storage unit 18. FIG. 12 shows theimplementation with a digital processor 1200 and digital memory 1210.The digital processor 1200 may be defined as the equivalent of a digitalsignal processor (DSP), general-purpose central processing unit (CPU),or a specialized CPU, including media processors. A likely DSP chip isone of the Texas Instruments TMS320 product line. A CPU could includeone of Intel's Pentium line or Motorola/IBM's PowerPC product line. Thedesign is straightforward for someone familiar with the state of the artgiven the pseudocode in FIGS. 5 through 9.

In addition, as shown in FIG. 13, a person familiar with the state ofthe art could implement the process with analog and digital circuitry,either separate or in an application specific integrated circuit (ASIC).The analog and digital circuitry could include any combination of thefollowing devices: a digital-to-analog converter (D/A), comparators,sample-and-hold circuits, delay elements, analog-to-digital converter(A/D), and programmable logic controllers (PLC). Someone familiar withthe state of the art given the previous description and pseudocode inFIGS. 5 through 9 could easily design the circuit.

FIGS. 11A and B show that the logic processor and storage unit typicallycomprise an embedding apparatus 700 and retrieving apparatus 770. Theembedding apparatus 700 includes the following. A data reader 710 toread original data 720 and auxiliary data 730. A A comparer 740, thatis, a circuit or device for comparing data points with known values orother data points. A data writer 750 to write the combined data 760 to apermanent or temporary storage media.

The retrieving apparatus 770 includes the following. A data reader 715to read the combined data. The data reader 715 may be identical to theembedding data reader 710, but it also may be different. A comparer 745,that is, a circuit or device for comparing data points with known valuesor other data points and, if necessary, producing the auxiliary bit orbits. Once again the comparer 745 may be identical or different that theembedding comparer 740. A data writer is not always necessary since theauxiliary information may be taken from memory or only displayed for thecorresponding use.

CONCLUSIONS, RAMIFICATIONS AND SCOPE

As the reader can see from the description above and determined fromtesting the process with CD quality audio, this process and apparatus ofhiding auxiliary information within original data is extremely efficientand has configurations which are non-perceivable. These advantages aremainly due to the invented process finding locations to hide theauxiliary data without needing to transform the signal to the frequencydomain and where masking may block or reduce the perception of theauxiliary data.

The foregoing descriptions of the preferred embodiments of the inventionhave been presented to teach those skilled in the art how to bestutilize the invention. Many modifications and variations are possible inlight of the above teaching. For example, as discussed above, the peakcriteria can be extended, the threshold may be dynamic, synchronizationcodes, error correcting codes, and any combination of peaks andthreshold can be used jointly. To this end, the following claims definethe scope and spirit of the invention.

1. A method comprising: utilizing an electronic processor programmed fortransmarking a media signal by acts of: detecting a first digitalwatermark in the media signal, the media signal being embedded with thefirst digital watermark using a first digital watermark embeddingmethod; embedding detected message information from the first digitalwatermark into a second digital watermark in the media signal before themedia signal undergoes a transformation process such that the seconddigital watermark is adapted to survive the transformation process. 2.The method of claim 1 wherein the second digital watermark is increasedin amplitude relative to the first digital watermark to survive thetransformation process.
 3. The method of claim 1 wherein the seconddigital watermark is embedded using a different steganographic embeddingmethod than the first digital watermark embedding method.
 4. The methodof claim 1 wherein the first digital watermark is partially removedbefore embedding the second digital watermark.
 5. The method of claim 1wherein the message information includes message symbols and furtherincluding: decoding the message symbols from the first watermark; andre-embedding the decoded message symbols from the first watermark intothe second watermark.
 6. The method of claim 5 wherein the messagesymbols include an index to a database entry that stores informationabout the media signal.
 7. The method of claim 5 wherein the messagesymbols include a content identifier.
 8. A non-transitory computerreadable medium comprising instructions stored thereon to cause anelectronic processor to perform the acts recited in claim
 1. 9. Aprogrammed computing device comprising instructions stored in memory,said instructions comprising instructions to cause said programmedcomputing device to perform the acts recited in claim
 1. 10. A method oftransmarking a media signal previously embedded with a first digitalwatermark using a first digital watermark embedding method, comprising:utilizing a programmed electronic processor, detecting the first digitalwatermark in the media signal; converting the media signal to adifferent format; utilizing a programmed electronic processor, embeddingdetected message information from the first digital watermark into asecond digital watermark in the converted media signal such that thesecond digital watermark is adapted to robustness or perceptibilityparameters associated with the new format.
 11. The method of claim 10wherein the new format is a compressed format of the media signal. 12.The method of claim 10 wherein the second digital watermark is encodedwith greater signal strength than the first digital watermark to survivetransformation of the media signal in the new format.
 13. The method ofclaim 10 wherein the second digital watermark is encoded with lessersignal strength than the first digital watermark so as to be lessperceptible in the new format of the media signal.
 14. The method ofclaim 10 wherein the first digital watermark is removed beforeconverting the media signal to the different format.
 15. Anon-transitory computer readable medium comprising instructions storedthereon to cause an electronic processor to perform the acts recited inclaim
 10. 16. A programmed computing device comprising instructionsstored in memory, said instructions comprising instructions to causesaid programmed computing device to perform the acts recited in claim10.
 17. An apparatus comprising: means for transmarking a media signalincluding: means for detecting a first digital watermark in the mediasignal, the media signal being embedded with the first digital watermarkusing a first digital watermark embedding method; means for embeddingdetected message information from the first digital watermark into asecond digital watermark in the media signal before the media signalundergoes a transformation process such that the second digitalwatermark is adapted to survive the transformation process.
 18. Anapparatus for transmarking a media signal previously embedded with afirst digital watermark using a first digital watermark embeddingmethod, said apparatus comprising: means for detecting the first digitalwatermark in the media signal; means for converting the media signal toa different format; means for embedding detected message informationfrom the first digital watermark into a second digital watermark in theconverted media signal such that the second digital watermark is adaptedto robustness or perceptibility parameters associated with the newformat.